Abnormal heart rate regulation in GIRK4 knockout mice.
Acetylcholine (ACh) released from the stimulated vagus nerve decreases heart rate via modulation of several types of ion channels expressed in cardiac pacemaker cells. Although the muscarinic-gated potassium channel I(KACh) has been implicated in vagally mediated heart rate regulation, questions concerning the extent of its contribution have remained unanswered. To assess the role of I(KACh) in heart rate regulation in vivo, we generated a mouse line deficient in I(KACh) by targeted disruption of the gene coding for GIRK4, one of the channel subunits. We analyzed heart rate and heart rate variability at rest and after pharmacological manipulation in unrestrained conscious mice using electrocardiogram (ECG) telemetry. We found that I(KACh) mediated approximately half of the negative chronotropic effects of vagal stimulation and adenosine on heart rate. In addition, this study indicates that I(KACh) is necessary for the fast fluctuations in heart rate responsible for beat-to-beat control of heart activity, both at rest and after vagal stimulation. Interestingly, noncholinergic systems also appear to modulate heart activity through I(KACh). Thus, I(KACh) is critical for effective heart rate regulation in mice.
Wickman
K
K
Department of Cardiology, Harvard Medical School, Children's Hospital, Boston, Massachusetts 02115, USA.
Nemec
J
J
Gendler
S J
SJ
Clapham
D E
DE
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D004562:Electrocardiography; D004594:Electrophysiology; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL / Q000235:genetics; D018345:Mice, Knockout / Q000235:genetics* / Q000502:physiology*; D009116:Muscarine / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000235:genetics* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D013268:Stimulation, Chemical; D013686:Telemetry; D014630:Vagus Nerve / Q000502:physiology
D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D009116:Muscarine; D000241:Adenosine